1. Field of the Invention
The present invention relates to an infrared data transmission-reception system capable of transmitting and receiving various kinds of data such as command data for remote-controlling electronic equipment.
2. Description of Prior Art
The conventional infrared data transmission-reception system comprising data transmitting means and data receiving means has widely been put to practical use as, for example, a remote operating means for controlling electronic equipment through an infrared remote controller. The data transmitting means is capable of generating various kinds of data in the form of infrared signals obtained as a result of modulating data bit pulses and the data receiving means is capable of obtaining predetermined data from the data bit pulses obtained by demodulating the infrared signals generated from the data transmitting means.
There are various types of electronic equipment such as a television receiver, disk player, VCR, air conditioner and etc., which can be operated by a distant user in various kinds of modes through a remote controller for generating infrared signals.
The remote controller exclusively used for the above-mentioned electronic equipment generates a command signal coded in a specific format in correspondence to the operation designated by the user and the command signal is then converted into an infrared signal by a light-emitting diode so as to be transmitted as an output to the electronic equipment. The electronic equipment is provided with an infrared receiving unit and a demodulating unit of which the former detects the outputted infrared signal and the latter demodulates the signal into an electrical command signal to be inputted to a system control unit which performs a control operation based on the command signal.
In FIG. 6, there is conceptually shown the structure of an infrared remote control system mounted in a monitor television receiver, stereo system amplifier and etc., wherein reference numeral 1 designates a remote controller as a data transmitting means which is provided with an operating key 1a and a rotary operating section 1b so as to allow the user to perform a predetermined operation by pressing the key or rotating the rotary section whereby predetermined control data (data bit pulses) is generated and outputted from an infrared output section 1c after the data is modulated.
On the other hand, designated by reference numeral 2 is an infrared receiving unit arranged within the body of the electronic equipment so as to act as a data receiving means. This unit 2 receives infrared control data generated from the remote controller 1 and demodulates it into an electrical signal. The demodulated control data (command signal) is then supplied to a microcomputer 3 as an equipment control means which latter supplies control signals to predetermined processing circuits (4a, 4b, 4c) such as an video signal processing unit, audio signal processing unit, tuning unit, power source circuit and etc. mounted in the electronic equipment, in accordance with the control data it receives, thereby performing predetermined processings.
The above-mentioned remote controller 1 as the data transmitting means and the infrared receiving unit 2 as the data receiving means are constructed as shown in FIGS. 7 and 8, for example.
Regarding the remote controller 1, when operation information is supplied to an encoder 11 from the operating key 1a or rotary operating section 1b, a train of data bit pulses as a command signal is outputted in correspondence to the operation and supplied to a modulation unit 12 which has a carrier of e.g., 40 kHz supplied from a carrier generating unit 13. In the modulation unit 12, the 40 kHz carrier is modulated by the train of data bit pulses from the encoder 11 and the modulated signal is supplied to an infrared output unit 14. Thus, when the modulating signal performs ON/OFF drive on a transistor T.sub.R, an infrared output corresponding to the modulating signal is obtained from a light-emitting diode D.
Meanwhile, the infrared receiving unit 2 receives the infrared output through its light-receiving section 21, and after converting the output into an electrical signal, supplies the converted signal to a detection circuit 23 through an amplification circuit 22 to thereby obtain a train of data bit pulses. The train of data bit pulses thus obtained is then decoded by a decoder 24 so that, for example, control data (a command signal) to be supplied to the microcomputer 3 may be obtained.
Recently, an inverter-based high-frequency fluorescent lamp has become widespread as an indoor illumination device. However, since such type of illumination device performs a lighting operation by using pulses of around 40 kHz, the infrared output from the illumination device has had a signal waveform quite similar to that of the infrared output (40 kHz carrier) from the remote controller 1 and accordingly, there has arisen a problem of the electronic equipment operating erroneously when the illumination device is lighted.
To meet this problem, it has been practiced that for example, the frequency band of the remote controller is shifted from that of the illumination device such that the carrier of the remote controller 1 is made to fall in the range of 33.about.40 kHz while the pulses from the illumination device fall within the range of 40.about.50 kHz, thereby avoiding the occurrence of mutual interference.
However, where the incident light is intense, the amplification circuit 22 of the infrared receiving unit 2 is saturated to become inoperative and when the inverter-based high-frequency fluorescent lamp has become further popularized and become versatile in type as having a plurality of unit lamps with a plurality of inverters, there arise beats among infrared pulses with, the wave form of the beats becoming quite similar to that of the infrared output of the remote controller 1 which results in that the command signal can not be distinguished from external noises causing the electronic equipment to operate erroneously and the accuracy of the remote-controlling operation can not be sufficiently maintained by mere division of the frequency band.
The data bit pulse modulating signal from the remote controller 1 comprises a train of bits as shown in FIG. 9(a) which is formed of a gathering of bursts of 33.about.40 kHz with a predetermined bit train forming one frame and the signal is outputted repeatedly per frame. The modulating signal comprising such frame unit bit train comes to be present at the output of the light-receiving section 21 of the infrared receiving unit 2 and is detected at a detection circuit 23 to thereby obtain the data bit pulses as shown in FIG. 9(b).
Next, where the infrared receiving unit 2 has received the infrared output from an inverter-based signal fluorescent lamp, a continuous 40 kHz level signal shown in FIG. 9(c) appears at the output of the light-receiving section 21 but when there is no alternating change, it is easy to make any detected output unobtainable. Further, although there is sometimes a case in which a detected output as shown in FIG. 9(d) appears due to a weak input of a level close to the operation-start level of the detection circuit 23 or due to an alternating fluctuation caused by a ripple on the fluorescent lamp power source, such output can be discriminated sufficiently at a decoder 24 because it is in the form of random pulses and it is therefore possible to avoid generation of any erroneous operation on the electronic equipment.
Now, where two fluorescent lamps are lighted with two inverters, respectively, both of the inverters generate stabilized sine waves (e.g., 45.000 kHz and 45.660 kHz) so that beats generate due to a frequency difference between infrared pulses and a ripple output having a beat frequency envelope formed therein as shown in FIG. 9(e) is outputted from the light-receiving section 21. This ripple output is generated as an accurate pulse train as shown in FIG. 9(f) at the detection circuit 23 and is sometimes decoded erroneously by the decoder 24. That is, it sometimes happens that an erroneous operation takes place on the electronic equipment.
Further, where an additional fluorescent lamp with an inverter of 45.010 kHz is lighted simultaneously with the above-mentioned two fluorescent lamps, the output of the light-receiving section 21 which has received the infrared outputs from these fluorescent lamps will be as shown in FIG. 9(g) so that the detected output will be as shown in FIG. 9(h). In other words, a predetermined frame period generates on the detected output so that the output becomes more similar to the infrared output from the remote controller 1 resulting in a great increase in the probability of generation of an erroneous operation.
Moreover, with an increase in the number of inverter-based fluorescent lamps lighted simultaneously, it becomes difficult for the infrared receiving unit 2 to distinguish between the infrared output from the remote controller and the noises from the fluorescent lamps.